It is an advantage to characterize a personalizable read-only memory using only a current source, as opposed to a voltage source, as the power increases as the value of the resistive fusable link increases. With a constant voltage source, the power employed to volatize the fusable link decreases as the value of the fusable link resistive element increases. Higher reliability in opening a desired predetermined fusable link is thus attained by employing constant current volatizing power sources.
In a memory matrix it is desirable to volatize only certain predetermined cell locations. Prior techniques for personalizing a memory often create "sneak paths" which allow fusable elements to be opened which are intended to remain intact. This problem is further compounded by the fact that the fusable elements in many programmable or personalizable read-only memories are typically in the range of 200 ohms and it takes anywhere from 30 to 40 milliamps to volatize or open the fusable links at 8 volts or greater. These voltage swings are incompatible with emitter coupled logic circuit type read-only memories which normally attain voltage swings in the range of 800 millivolts.
It is therefore an object of the present invention to provide a personalizable or programmable read-only memory which can reliably select the fusable element to be opened using emitter type logic and then readily allow the selected memory location to be volatized by an auxiliary current source so as to increase the likelihood of complete volatilization or opening of the fusable link.